“…This was in agreement with thermal diffusivity measurements along these axes reported earlier (Gaffar et al, 1987). Ferroelectric crystals, which exhibit incommensurate phase transitions include ammonium fluroberrylate (Iizumi & Gesi, 1977), potassium selenate , sodium nitrite (Yamada et al, 1963), thiourea (Goldsmith & White, 1959) etc. Thiourea, with the chemical formula SC (NH 2 ) 2 , undergoes successive phase transitions at 169 K (T 1 ), 176 K (T 2 ), 180 K (T 3 ) and 202 K (T 4 ).…”